How to Locate Underground Wires

Beneath our cities, towns, and neighborhoods lies a complex web of wire and cable. Made up of our our communication and power lines, these utility networks bring everything from energy to information and entertainment directly into our homes and businesses from around the globe.

Everyone is familiar with the sight of power and utility poles strung along streets and highways. Mirroring these visible wires and cables is often an even larger grid located under streets, sidewalks, and lawns.

Why Are Wires Located Underground

There are many reasons why utility companies prefer to bury wires and cables underground. One is that buried cables are far less likely to be damaged by weather events. Hurricanes, freezing rains, and falling tree limbs rarely affect utility lines buried beneath the ground.

Another reason why utility companies may want to bury lines is to keep in line with the city codes and ordinances designed to prevent excessive utility infrastructure from becoming an eyesore. In addition, although placing wires underground may be more expensive in terms of initial labor, the long-term benefits often outweigh the upfront costs.

Types of Underground Wires

There are many types of cable and wire used by utility companies. Different utilities will need different types of transfer cables, and the amount of data or power being transferred will require different sizes and material compositions.

Electric Cables:

Underground electric cables are classified by five features: the number of conductors in the cable, the voltage rating of the cable, the construction of the cable, the type and thickness of the insulation, and the installation method used. The voltage rating on underground electric wires can range from less than 1 kV to over 132 kV.

Fiber Optic Cables:

Underground fiber optic cables are classified by fiber type and by the number of fibers bundled in a cable. Fiber types are either single mode or multimode. Singlemode fiber is more useful over long distances as less refraction and reflection can occur to distort the signal. Multimode fiber is more useful for shorter distances where large amounts of data need to be transferred concurrently.

Television Cables

Cable television is not as widespread as it used to be, but many households still use direct cable television connections. These connections are frequently made using an underground line tied directly to the cable grid.

Why Locate Underground Wires

Occasionally, a buried wire or cable may be damaged during construction or excavation. This is known as a “line strike”. A line strike can be very dangerous if it involves an underground electrical cable. It can also be very expensive to repair or replace. To avoid line strikes, responsible contractors and others who dig should locate utilities before breaking ground. Alternatively, they may have others locate the lines for them.

In addition to avoiding line strikes, workers may wish to locate underground lines to work on repairs or to make replacements of existing utility lines.

Difficulties in Locating Underground Wires

When underground cables are installed today, the installation is usually swiftly mapped into computer software systems using GIS satellite systems. Unfortunately, this technology was not available for the installation of older systems and if mapping occurred at all, it was generally done with a pen and paper.

For many utility providers, these older maps can be notoriously unreliable, and many smaller organizations have traditionally relied on the knowledge of senior employees to find underground wire locations. The downside to this is that, as the older generation of workers retire, the knowledge they have of system locations can be lost. This leaves new utility employees in the dark when lines must be repaired or replaced.

Tools for Finding Underground Wires

Fortunately, a variety of wire and cable location tools are available to utility professionals. These locators can help eliminate time consuming and expensive guesswork on repair and replacement projects. The type of locator used is dependent on several factors including the material of line being that is being located, the presence or absence of trace wires, and the environment in which a cable is buried.

Traced vs Non-Traced Underground Wires and Cables

For the purposes of locating underground lines, cable materials can be divided into two broad categories: conductive and non-conductive. Conductive lines allow electrical signals to be transmitted along the length of a line. Materials for these wires and cables are often copper, steel, or aluminum. Non-conductive cable materials include most fiber optic lines.

Non-conductive lines can be more difficult to locate, and fiberoptic engineers often install copper trace wires along sections of non-conductive cables to help in future locating efforts. The presence or absence of trace wires or conductive materials will determine which line locating device is most appropriate for the job at hand.

Utility Locators

Utility locators have long been the industry workhorse for finding conductive and traced non-conductive wires and cables. Utility locators work by projecting an electromagnetic signal along the length of a line or cable with a transmitter device. A receiver wand is then used to scan the ground along the length of the line and to interpret the signal received from the transmitter.

Utility locator transmitters can create a signal along a line using either conduction or induction.

Conduction: Involves a direct connection between the transmitter and the cable or trace wire. This is usually done with connector cables. A ground stake is also used to complete the circuit. Direct transmitter conduction is usually more powerful than induction and allows a line to be traced at a further distance from the transmitter box.

Induction: involves indirect signal transmission. To use the induction method, the locator transmitter box is placed over the wire to be traced and set to emit an electromagnetic signal into the ground. The emitted signal then induces an electromagnetic signal along the cable or trace wire. Induced signals usually do not travel as far along wires as direct connection signals. This is due to a large amount of the transmitter wattage being expended in projecting the signal through soil or air.

For wires or cables located inside a PVC or other non-conductive housing and for cables where the protective coating cannot be breached to make direct contact, a transmitter clamp can be used to induce a signal onto the line.

Utility locators are very accurate and can even provide an estimate of the wire depth. However, they are of limited use if the line is non-conductive or if the trace wire has been broken.

AML / All Material Locators

All Material Locators or “AMLs” are useful for locating large diameter cables, or the sides of cable trenches. These devices are produced with proprietary technology by Subsurface Instruments. An AML works by projecting an ultra-high radio frequency into the ground. When a signal is reflected back to the receiver, it is interpreted by an onboard computer and the operator is alerted to any density change.

This technology allows the user to search for any item with a density different than the surrounding environment. This can include both conductive and non-conductive wires and cables. These locators are an excellent all-around tool for identifying all types of underground lines in areas that are relatively free of other buried materials such as rocks, concrete, and tree roots.

If a project requires the location of iron or steel materials as well as underground wires, Subsurface Instruments produces a combination utility locator / magnetic locator known as the PL-TT. This powerful locator incorporates the advantages of both a magnetic locator and traditional utility locator systems.

Choosing the Right Locator for Underground Wires

When considering purchasing an underground wire or cable locating device, the most important considerations are what type of cable material will you be locating and what environment do you expect it to be buried in. For most conductive utility lines made of a metal such as copper, steel, or aluminum, a utility locator is likely going to be the best choice.

For fiber optic cable location, the locating device will be determined by whether the line is equipped with a trace wire. If there is a trace wire, a traditional utility locator will still be the best option. If there is no trace wire, or if you suspect that the trace wire is broken, there are two options.

If it is believed that a fiber optic cable has a broken trace wire, a ground fault locator such as the A-Frame by Subsurface Instruments can help to locate the trace wire break for repairs. The A-Frame can also be used to locate breaks in underground conductive wires such as power or telephone.

If there is no trace wire, an All Materials Locator or AML should be considered, especially if the fiber optic cable is not buried in rocky soil or near tree roots.

For an all-around locator kit that can cover any underground wire locating situation, consider a combination of a traditional Utility Locator and the AML Plus All Material Locator.

Should You Locate Underground Wires Yourself?

Due to the potential for high voltage electrical shocks, line strikes can be very expensive and very dangerous. It is always advisable that electric and other utility lines are located prior to breaking ground on a project.

Utility location services are generally provided free of charge through your state’s 811 telephone line. Calling 811 automatically routes you directly to your local 811 center and each state has its own specific locating guidelines. If your state accepts online requests from homeowners and contractors, you may be able to file an “online request”.

If you are a contractor, or a utility service provider, utility location tools can also be useful devices for double checking locations provided by the 811 service. A second reading is never out of place and ensures that all underground wires and cables have been located properly. Having a utility locator on hand can also be useful in time sensitive projects where an 811 technician may not be able to arrive immediately.

Contact Us with Questions about Underground Wire and Cable Locators

If you are deciding on whether to purchase a locator for underground wires or cables, please feel free to reach out to us at Precision Outdoor Tech. We will discuss your needs and project specifications and will point you in the right direction to a line of products that can help you to locate your lines. Give us a call with your questions, and we will be happy to help you out. If it is after hours, please use the contact form listed in the municipal contact section below and we will respond shortly.

If you have already decided on the type of locator that you would like to use for your underground wire location projects, you can find our product collections via the following links.

Utility Locators

Utility locators work great for tracing metal wires or trace-wire equipped fiber optic lines.

All Material Locators (AMLs)

For all underground wire or cable types, including non-conductive materials. All Material Locators work best in non-rocky soils away from tree roots.